A four-year-old can be immersed in play.
When my son meets school-friends at playgrounds, they often play tag.* As seasoned tag players know, there are many variations. One striking feature of the game is that they sometimes change variants in mid play just in virtue of somebody calling out a new rule. Rather than seeing this as a violation of fair play (my spectatorial reaction), the other kids adjust quickly often seamlessly and with mental agility, but not always--sometimes there is resistance and the game halts. In principle, whole new rules can be introduced in mid play, but if there are more than a few kids this tends to stop the flow of the game. There are, of course, games of tag that have ultimate winners, and that approximate war-games, but the four to five year olds that play with my son favor the indefinite type of game of tag. The point of tag is to stay in that joyful flow. (That's compatible with momentary anguish and fear, of course.)
As an aside, the moralists and humanitarians are right that there is too much injustice and cruelty in the world. But at the risk of giving offense, the most damning thing that can be said about our political and economic orders is that even among the privileged, we do not cultivate joyful flow, which would be self-justifying, and encourage the substitution of practices that facilitate delusion about this. Among the saddest sights is to see otherwise capable adults embrace escapist activity that they claim generates joy, but that produces loneliness and anxiety. (Fill in your favorite exemplars.) Sometimes it takes a novelist to show us this sight, and then turn it into comedy.
At the playground, when new rules are introduced in mid-play, the game may halt for 'discussion.' This is a fragile moment--things can as easily devolve into mutual recrimination or into a cascading laughing fit. It's not to deny that 'discussion' can restore the game, but it never appears to be a foregone conclusion.
I suggested above that joyful immersion is self-justifying. It is lunacy to stop a game of tag and ask, 'why are you playing this game.'** The practice of philosophy is self-justifying like that. Of course, this way of conceiving philosophy falls short of the demands of morality, the market-place, and the needs of the powerful. So, we graft onto this play ulterior, often noble ends, which risk displacing play altogether. Sometimes we unify these other ends by appeal to 'truth;' undeniably there are lots of important truths about play, but there is also a non-trivial sense in which truth and even justice are absent amidst play.
Sometimes, when the kids meet each other, they start bragging shamelessly about age and height: 'How old are you' 'Four' 'I am Five.' 'I am taller' I will be eleven when you are 10.' 'I will be even taller then.' 'Even when you are twenty-eight, I'll be twenty-nine.' And so on trumping each other through eternity and space. [I have no idea if this is a universal phenomena, or particular to class and country.] This bragging is compatible with lots of play, even fun, although I have never seen it while they are playing tag. The other day may son was trumping a friend in age and height while they were playing at the gate of the playground. Just as my son thought he could relax, the friend responded by yanking the gate closed on one of my son's fingers.
*Within analytical philosophy we have quickly forgotten how controversial Lewis once was, but as recent as a generation ago his approach to philosophy was often denounced. Obviously, part of the ire was generated by his breaking the taboo on metaphysics (and for embracing a purportedly unscientific metaphysics); but I have come to suspect that his real crime was showing that serious play is possible within analysis. (Obviously, this footnote requires considerable development because jokes, puns, and humor have always been a part of analytical philosophy.)
**Of course, sometimes kids are afraid to 'jump in,' and one may need to subtly insert them into the game without ruining the flow. Generally playground tag is robust relative to number of players.